Simple demonstration microscope made by Engell.
Inside the cover:
Ocular & Linsen-Systeme von E. Hartnack
G. Oberhäuser in Paris.
Schaeffer & Budenberg
In this simple microscope, the coarse focus is obtained by the sliding tube, while the fine focus is achieved by a screw on the side of the optical tube. The objective is of the "Lieberkühn" type. When in use, the slide is positioned in a groove and the rotated to fix it firmly (see picture on the right). Then, it was pointed toward a light source (for example the sky); in this way many people could observe the specimen passing the instrument hand by hand.
Within the cover there is a decorative paper, reporting as the lens system was due to Hartnack, one of the most famous lens-maker of the time, in turn Oberhauser successor.